How to Detect STL Containers Using Type Traits in C ?

Detecting STL Containers Using Type Traits

Introduction

A type trait is a powerful tool in C that evaluates the properties of a type at compile time. In this question, we aim to construct a type trait (is_vector or is_container) that discerns various common STL container types.

Solution for is_vector

The provided implementation for is_vector encounters an error as it does not utilize the template parameter U. To rectify this, here's a revised version:

<code class="cpp">template<class T>
struct is_vector {
  static bool const value = false;
};

template<class U>
struct is_vector<std::vector<U>> {
  static bool const value = true;
};</code>

Generalizing to is_container

Expanding on the is_vector concept, we can create a generic is_container trait that identifies various STL container types:

<code class="cpp">template<typename T, typename _ = void>
struct is_container : std::false_type {};

template<typename... Ts>
struct is_container_helper {};

template<typename T>
struct is_container<
        T,
        std::conditional_t<
            false,
            is_container_helper<
                typename T::value_type,
                typename T::size_type,
                typename T::iterator,
                decltype(std::declval<T>().size()),
                decltype(std::declval<T>().begin()),
                decltype(std::declval<T>().end())
                >,
            void
            >
        > : public std::true_type {};</code>

This improved is_container trait can be customized to check for additional container-specific characteristics or restricted to only STL containers by verifying the presence of specific member functions and types.

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